1. Field of the Invention
The present invention relates to a radio frame control apparatus, a radio frame control method, and a radio communication apparatus.
Priority is claimed on Japanese Patent Application No. 2007-093760, filed Mar. 30, 2007, the content of which is incorporated herein by reference.
2. Description of Related Art
As a next-generation wireless access system, IEEE 802.16 serving as an Institute of Electrical and Electronic Engineers (IEEE) standard for realizing a high-speed broadband transmission (for example, see IEEE Std 802.16-2004, “Air Interface for Fixed Broadband Wireless Access Systems,” 2004). In the IEEE 802.16 standard, an Orthogonal Frequency Division Multiple Access (OFDMA) system is adopted as a transmission system. The OFDMA system is a multicarrier transmission system for performing communication using a broadband signal configured from a plurality of subcarriers whose frequencies are orthogonal to each other, and realizes multiple accesses between one base station and multiple users by using different subcarriers between users (terminal stations). As an extension of the IEEE 802.16 standard, an IEEE 802.16e standard for a mobile communication environment is defined (for example, see IEEE Std 802.16e-2005, “Air Interface for Fixed Broadband Wireless Access Systems,” 2005.). Similarly, also in the IEEE 802.16e standard, the OFDMA system is adopted as a transmission system.
FIG. 5 shows a conventional configuration example of a radio frame of an uplink (link from a terminal station to a base station) (hereinafter, referred to as “uplink subframe”). The uplink subframe of FIG. 5 is based on the IEEE 802.16 and IEEE 802.16e standards (hereinafter, both the standards are referred to as the IEEE 802.16 standard or the like).
In FIG. 5, the uplink subframe is configured from a plurality of OFDMA symbols and a plurality of logical subchannels. In the uplink subframe, the plurality of OFDMA symbols are multiplexed in a time axis direction over an uplink subframe duration. Moreover, in an OFDMA symbol, a plurality of subchannels are frequency multiplexed.
In the OFDMA system, placement information indicating whether to arrange a packet from each user in a logical subchannel of an OFDMA symbol is determined on an uplink subframe basis. The base station notifies each terminal station of the determined placement information through downlink communication. A transmitter of each terminal station performs an uplink packet transmission using a logical subchannel designated in the notified placement information.
An uplink packet from each terminal station arranged in the logical subchannel is transmitted after being rearranged in a frequency axis direction upon actual transmission. In the IEEE 802.16e standard, a rearrangement pattern is designated with a parameter called uplink permbase (UL_Permbase). UL_Permbase is defined by designating values from 0 to 69, and the rearrangement pattern differs according to the values. Each terminal station converts data displaced in a logical subchannel in a pattern based on the UL_Permbase value into an arrangement on an actual frequency and then performs a transmission.
FIG. 5 shows a Partial Usage of SubChannels (PUSC) zone of an uplink subframe of the IEEE 802.16 standard or the like. As shown in the same figure, a ranging subchannel and an uplink burst (UL burst) are placed in the uplink subframe. The ranging subchannel is a part for storing a signal for transmitting an access request when a terminal station accesses a base station or transmitting a band request after access. The UL burst is a part for storing a packet of actual communication and one UL Burst is configured with an uplink packet from one terminal station. For the UL burst, its size can be arbitrarily determined within a limit defined in the IEEE 802.16 or the like. In FIG. 5, five UL bursts for the uplink are arranged. The arrangement method is based on the IEEE 802.16 standard or the like.
FIG. 6 shows an example of a relationship between placement information reported to a terminal station side and an uplink burst on a radio frame in the related art. As shown in FIG. 6, the placement information is configured with three information elements of a communication identifier, a modulation scheme and coding rate (PHY_MODE), and a resource amount, available in a packet transmission, assigned to corresponding communications, and a resource amount for one communication identifier within the placement information corresponds to a definition of one uplink burst on a radio frame.
However, the IEEE 802.16 standard or the like defines a method for assigning OFDMA symbols and subcarriers, that is, an uplink burst arrangement method. According to the definition, one burst secures a resource in ascending order of logical subchannel numbers as in a burst configuration shown in UL Burst #2 of FIG. 5. In one logical subchannel, a resource is secured in a time axis direction (OFDMA symbol direction). A resource is secured subsequent to the end of a previous burst, such that a packet is to be assigned in the resource.
That is, a resource used for each communication indicated by a communication identifier within the placement information is to be secured from a resource immediately after a resource used by the previous communication according to a sequence indicated in the placement information. A resource amount used by each communication corresponds to a resource amount designated in the placement information. The position and size of each uplink burst are determined by two information elements.
For example, since the communication of a communication identifier 1 is assigned 11 slots as an available resource amount in FIG. 6, a packet is transmitted using slots from a first slot of the No. 2 logical subchannel serving as the next channel of the No. 1 logical subchannel secured by a ranging subchannel to the third slot of the No. 4 logical subchannel. Since the communication of a communication identifier 2 is assigned 14 slots as an available resource amount, a packet is transmitted using slots from the fourth slot of the No. 4 logical subchannel immediately after a resource used by the communication of the communication identifier 1 to the first slot of the No. 8 logical subchannel. Since the communication of a communication identifier 3 is assigned 19 slots as an available resource amount, a packet is transmitted using slots from a second slot of the No. 8 logical subchannel immediately after a resource used by the communication of the communication identifier 2 to the last slot of the No. 12 logical subchannel. Since the communication of a communication identifier 4 is assigned 14 slots as an available resource amount, a packet is transmitted using slots from the first slot of the No. 13 logical subchannel immediately after a resource used by the communication of the communication identifier 3 to a second slot of the No. 16 logical subchannel. Since the communication of a communication identifier 5 is assigned 14 slots as an available resource amount, a packet is transmitted using slots from the third slot of the No. 16 logical subchannel immediately after a resource used by the communication of the communication identifier 4 to the last slot of the No. 19 logical subchannel.
For this reason, there is a problem in that a radio frame, in which an empty slot and an empty logical subchannel are present before an uplink burst, may not be conventionally configured. Also in the case when there is a logical subchannel of a bad radio wave environment or an unused logical subchannel, there is a problem in that a radio frame, in which an empty slot and an empty logical subchannel are present, may not be configured.